Update documentation about add index.md files inside children.

[Barbapapazes]

Environment

/

Reproduction

/

Describe the bug

If you add an index.md file inside a folder, it will be added inside the children from the navigation part.

Additional context

No response

Logs

No response

[christophermiles]

Agree, I don't understand what the convention is meant to be here. I've followed the example from the documentation and now I have a bizarre navigation tree that has each page being its own child.